Carbon paper having barrier coat of concentrated sulfite waste liquor



United States Patent 3,508,948 CARBON PAPER HAVING BARRIER COAT OF CONCENTRATED SULFITE WASTE LIQUOR Warren A. Lemke, Glens Falls, and Jerry J. Iannucci, Hudson Falls, N.Y., assiguors to International Paper Company, New York, N.Y., a corporation of New York No Drawing. Filed June 22, 1966, Ser. No. 559,413, Int. Cl. B41b 5/10; B41c 1/06 US. Cl. 11736.4 6 Claims ABSTRACT OF THE DISCLOSURE A carbon paper having improved carbon release when subjected to pressure consisting of carbon dope and carbonizing tissue made from lightly refined pulps and barrier coated with water-soluble concentrated sulfite waste liquor alone or in combination with a water-soluble resin such as polyvinyl alcohol.

This invention relates to carbon paper. More particularly, it relates to a new and useful process of preparing one-time carbon paper and the product thereof.

Carbon paper for office use, particularly that produced for use once only in business forms and the like, involves the combination of carbon dope and carbonizing tissue paper. In the preparation of the carbon dope, a mixture of pigments, dyes, waxes (e.g., mountain, beeswax, candelilla), and mineral oil is ground up while in a heated state and blended'in a ball mill. Using a roll applicator and doctor rod or a roll coater, the hot, blended mixture is applied in molten form to the carbonizing tissue sheet or web and, immediately after such application, is chilled to set it on the tissue. Thereafter, the carbonized tissue is, typically, manifolded, interleaved with register grade paper, punched and perforated, and otherwise manipulated in the production of business forms.

It is the current commercial practice to begin preparing carbonizing paper by refining pulps derived from wood to a very low Canadian standard freeness (C.S-.F.), i.e., by refining them so that water drains from them slowly, cf., Calkin, J. B.; Modern Pulp and Paper Making (3rd ed.); Reinhold Publishing Corporation; New York, 1957; p. 481. By means of beaters or continuous flow refining engines, the pulp is refined from an initial freeness of about 600 ml., C.S.F., to a final freeness of about 25 ml., C.S.F. Paper made from such a pulp is dense and closedup. It will have a Gurley porosity of over 250 closedand pinholes (determined by ink smear) in the range of 250 or more per square foot. Cf., Sutermeister, E.; Chemistry of Pulp and Paper Making (3rd ed.); John Wiley & Sons, Inc.; New York, 1941; pp. 457 and 458 and Mosher, R. H.; Specialty Paper; Remsen Press; Brooklyn, 1950; p. 342 et seq.

Carbonizing tissue which is dense and closed-up presents several disadvantages in the manufacture of carbon paper. The paper is expensive to make, because of the large amount of powder required to refine the pulp. From 35 to 50 horsepower days per ton are required to refine such pulp. Again, because of the very low freeness of the pulp, drainage of Water from the stock as it is passed over the Fourdrinier or other paper machine is very slow and the machine speed is also slowed, adding to the cost of the manufacture of the paper.

A way has now been found to produce carbon paper more economically and at higher speeds. This involves,

3,508,948 Patented Apr. 28, 1970 on the one hand, a carbonizing tissue sheet made from pulps refined to a much lesser degree, e.g., 400 ml., C.S.F., which can be produced at roughly greater speed on a paper machine and have a Gurley porosity in the range of about 1 to 5 seconds. And, on the other hand, it involves resort to a barrier coating on such carbonizing tissue to overcome some of its inherent disadvantages. For, a sheet made from lightly refined pulps is open and has a lacy structure with a very large number of pinholes. Its porosity as measured by the Gurley instrument is of the order of 5 seconds or less and, when it is carbon dope-coated, it absorbs the coating and evidences considerable bleed-through. In practical terms, it consumes an excess amount of carbon dope, it makes for messy carbon paper, and it is characterized by poor release of the carbon dope when subjected to writing pressure or typewriter impact.

It has now been found, then, that use of a barrier coating on a less or partially refined one-time carbonizing tissue substrate prior to applying carbon dope thereto increases the Gurley porosity of the sheet, seals off its surface, prevents penetration of excess carbon dope, and gives excellent carbon release when subjected to pressure. Particularly is this so when the barrier coating is comprised of concentrated sulfite waste liquor alone or combined with a small amount (i.e., about 1% by weight of the concentrated sulfite waste liquor, dry solids basis) of a water-soluble resin such as polyvinyl alcohol, polyacrylamide, or the like.

The concentrated sulfite waste liquor barrier coating employed in the present invention is a by-product of the acid sulfite process for pulping wood and contains sulfonated lignin materials. More particularly, it mainly contains the salts of lignosulfonic acid. Simple sugars can also be present; the operation of the herein-claimed invention does not depend on the absence or presence of such simple sugars.

By way of example, one-time carbon paper having almost 100% release of the carbon under pressure and coating substantially less than present-day commercial products is made by applying two to three pounds of about 50% solids Bindarene, a commercially available concentrated sulfite waste liquor, to a 25 x 36-500 ream of porous carbonizing tissue having an initial Gurley porosity of 5 seconds or less. This application increases the Gurley porosity of the sheet to over 200 seconds and reduces the number of pinholes therein to about 200 or less per square foot. The thus-barrier coated sheet is then coated with a conventional carbon dope in the conventional way. Tests show that the carbonizing wax layer is held on the surface of the sheet and that there is little penetration through the pinholes.

What is claimed is:

1. A carbon paper comprising a carbonizing tissue having a Gurley porosity in the range of about 1 to 5 seconds, a barrier coating of concentrated sulfite waste liquor disposed on the carbonizing tissue, and a carbon dope coating disposed on the barrier coating.

2. The carbon paper of claim 1 wherein the barrier coating is water-soluble concentrated sulfite waste liquor.

3. The carbon paper of claim 2 wherein the barrier coating is 50% solids concentrated sulfite waste liquor applied to the carbonizing tissue at a rate of from about 2 to 3 pounds per 24 x 36500 ream of carbonizing tissue.

4. The carbon paper of claim 2 wherein the barrier coating is concentrated sulfite waste liquor and a water- 3 4 soluble resin amounting to about 1% by Weight of the 2,606,775 12/1952 Newman 11736.4 concentrated sulfite waste liquor, dry solids basis. 2,824,815 2/1958 -Dow11s et a1 117--36.4 5. The carbon paper of claim 4 wherein the water- 3,376,154 4/1968 C b ll et 1 117 36 4 soluble resin is polyvinyl alcohol.

6. The carbon paper of claim 4 wherein the water- 5 OTHER REFERENCES soluble resm ls polyacrylamlde' Specialty Papers, Mosher, 1950, Rernsen Press, Brook- References Cited Page UNITED STATES PATENTS MURRAY KATZ, Primary Examiner 1,231,153 6/1917 Haefiner 162-163 10 2,063,226 12/1936 Braunstein 117--36.4 US. Cl. X.R.

2,348,128 5/1944 Groak 11736.4 117 --76, 92 

